Combined point of care nucleic acid and antibody testing for SARS-CoV-2: a prospective cohort study in suspected moderate to severe COVID-19 disease.

Abstract Background Rapid COVID-19 diagnosis in hospital is essential for patient management and identification of infectious patients to limit the potential for nosocomial transmission. The diagnosis is complicated by 30-50% of COVID-19 hospital admissions with negative nose/throat swabs negative for SARS-CoV-2 nucleic acid, frequently after the first week of illness when SARS-CoV-2 antibody responses become detectable. We assessed the diagnostic accuracy of combined rapid antibody point of care (POC) and nucleic acid assays for suspected COVID-19 disease in the emergency department. Methods We developed (i) an in vitro neutralization assay using a lentivirus expressing a genome encoding luciferase and pseudotyped with spike protein and (ii) an ELISA test to detect IgG antibodies to nucleocapsid (N) and spike (S) proteins from SARS-CoV-2. We tested two promising candidate lateral flow rapid fingerprick test with bands for IgG and IgM. We then prospectively recruited participants with suspected moderate to severe COVID-19 and tested for SARS-CoV-2 nucleic acid in a combined nasal/throat swab using the standard laboratory RT-PCR and a validated rapid nucleic acid test. Additionally, serum collected at admission was retrospectively tested by in vitro neutralization, ELISA and the candidate POC antibody tests. We determined the sensitivity and specificity of the individual and combined rapid POC diagnostic tests against a composite gold standard of neutralisation and the standard laboratory RT-PCR. Results 45 participants had specimens tested for nucleic acid in nose/throat swabs as well as stored sera for antibodies. Serum neutralisation assay, SARS-CoV-2 Spike IgG ELISA and the POC antibody test results were concordant. Using the composite gold standard, prevalence of COVID-19 disease was 53.3% (24/45). Median age was 73.5 (IQR 54.0-86.5) years in those with COVID-19 disease by our gold standard and 63.0 (IQR 41.0-72.0) years in those without disease. Median duration of symptoms was 7 days (IQR 1-8) in those with infection. The overall sensitivity of rapid NAAT diagnosis was 79.2% (95CI 57.8-92.9%) and 50.0% (11.8-88.2) at days 8-28. Sensitivity and specificity of the combined rapid POC diagnostic tests reached 100% (95CI 85.8-100) and 94.7% (95CI 74.0-99.0) overall. Conclusions Dual point of care SARS-CoV-2 testing can significantly improve diagnostic sensitivity, whilst maintaining high specificity. Rapid combined tests have the potential to transform our management of COVID-19, including inflammatory manifestations where nucleic acid test results are negative. A rapid combined approach will also aid recruitment into clinical trials and in prescribing therapeutics, particularly where potentially harmful immune modulators (including steroids) are used.